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THE MIOCENE TREES OF THE ROCKY
PROFESSOR T. D. A. COCKERELL
University of Colorado.
The living arborescent flora of the Rocky Mountain
region is at the present time occupying the attention of
a number of able workers, including Nelson in Wyoming,
Rydberg of the New York Botanical Garden, Sudworth
of the Forest Service, Ramaley, Bethel and Schneider in
Colorado, Wooton in New Mexico, and others. As a re-
sult of all this activity, we are promised two manuals of
Rocky Mountain botany, and a third of trees alone, so
we shall have three separate and independent treatments
of our woody flora to compare and choose from.
Unfortunately, those who have been so active and ex-
haustive in their investigations of the living flora have
not cared, as a rule, to consider the historical or paleo-
botanical side of the subject. Many " recent " botanists
seem to have a positive dislike for fossil plants, and few
manifest any great eagerness to receive information
about the ancestors or predecessors of the species which
occupy their attention. Like all enthusiasts, the writer
is filled with the idea that the matter has only to be ade-
quately presented to command universal attention; and
hence offers this discussion, not so much for the paleo-
botanists as for those students of living plants whose
active interest may be aroused in the problems involved.
Going back from the present time, we are practically
without information concerning the plants of our region
until we come to the Florissant beds, assigned to the
Miocene. These beds, however, contain an abundant
series of remains, many of the plants beautifully pre-
served, as the accompanying illustrations show. They
testify to a climate both warmer and damper than that
of the present day, the arborescent genera including
Sapindus, Ficus, 1 Diospyros, Persea, Leucasna, Anona,
1 The determination of Ficus is based on the leaves. In confirmation of
32 THE AMERICAN NATURALIST [Vol. XLIV
etc., but so far as known no palms. Some, as Ailantlins
americcma, pertain to genera now restricted to Asia.
The determination of the age of the Florissant beds
has been a matter of some difficulty, notwithstanding the
large number of organisms preserved. Comparing the
flora with that of the European Tertiary, I have felt
satisfied that it should be referred to the Miocene, and
probably to the Upper Miocene. The resemblance to the
flora of GEningen in Baden, known to be upper Miocene,
is most striking. Thus we have the following parallel
or representative species :
Liquklambar eonvexum Ckll. Liquiclambar europccum A. Br.
TJlmus braiinii Heer, Lx. Ulmiis braunii Heer.
Comptonia insignis (Lx.) Ckll. Comptonia amingensis A. Br.
For ana spcirii Lx. Porana cening crisis A. Br.
Parana tenuis Lx. Porana macrantlia Heer.
Acer florissanti Kirch. Acer tri cuspid latum A. Br. 2
Many others could be cited. On the other hand, the
Florissant incense cedar, Heyderia or Libocedrus colo-
radensis Ckll., is to be compared with H. salicornioides,
of the Low T er Miocene of Radoboj in Croatia. The
Florissant redwood, Sequoia haydeni (Lx.), is not related
to 8. sternbergi Heer from GEningen, but to 8. langsdorfii
(Brgt.) Heer of the Swiss Lower Miocene; this species,
however, survived into the Upper Miocene in Italy and
Galicia. This 8. langsdorfii has been recognized in
America also from the Upper Cretaceous to the Miocene,
and some of the Florissant specimens have been referred
to it; but the identity of the plants from so many diverse
localities and horizons is questionable, and from Floris-
sant I think we have only one species, 8. haydeni.
The Sequoia and Libocedrus of Florissant are both
very closely related to their living Californian allies; so
it comes a discovery by Mr. Brues, who in working over the parasitic Hymen-
optera from Florissant has come upon what appears to be a genuine fig-
insect,, apparently of the South American genus Tetrapus Mayr.
-Acer trilobatum (Sternb., 1825) A. Br., 1845; not A. trilobatum Lam.,
No. 517] MIOCENE TREES 33
much so that one is in some difficulty to point out any
tangible differences. This is equally true of a number
of other cases, of which the following are illustrative :
Finns ivlieeleri Ckll. Finns flexilis James.
Finns sPurgisi Ckll. Finns tee da L.
Ailanthus americana Ckll. Ailanthus glandnlosa L.
Sambucus newtoni Ckll. Sambucus arboreseens Nutt.
Anona spoliata Ckll. Anona glabra L.
Bobinia brittoni Ckll. Bobinia pseudacacia L.
Fopuhis lesquereuxi Ckll. Fopulus angust-i folia James.
Quercus lyratiformis Ckll. Quercus 1 grata Walt.
Sapindus coloradensis Ckll. Saj)indus drummondi H. & A.
So numerous are the resemblances to the living flora
that one might well feel persuaded to refer the beds to
the Pliocene— certainly better there than to the Oligocene
or Eocene ! However, the Florissant fishes, with the
exception of Anna, are of extinct genera, and no less
than 178 genera of insects are supposed to be extinct.
For a variety of reasons, based chiefly upon a study of
the insects, I believe that the Florissant period corre-
sponds with Oshorn's "Fifth Faunal Phase" (Bull. 361,
II. S. G-eol. Survey), in which a new fauna was invading
the country from Eurasia, while connection with South
America had not yet been established. Some of the
Florissant groups of insects, such as the Aphididre and
Bombyliida?., seem to represent the original American
fauna uncontaminated ; while others show old world
types, the most significant and interesting of which is
the tsetse fly (Glosshia)* Osborn's "Fifth Phase " in-
cludes the Middle and Upper Miocene, and so far as may
be judged, Florissant should belong near the middle
The attempt to correlate the Florissant beds with other
American floras ascribed to the Miocene brought out a
number of difficulties. With the exception of the little-
3 A second species of tsetse fly, Gloss ha osborni Ckll., lias been recently
discovered. It is only ICU mm. long, the wing 7 mm.; the venation is normal
for the genus, but the first basal cell bulges less subapically than in Scud-
THE AMEBIC AN NATURALIST [Vol. XLIV
Fig. 2. Weinmannia lesquereuxi Ckll. Fig. 1. Weinmannia phenacophylla Ckll.
known formation at Elko Station, Nevada, I do not find
anything which really seems to correspond with Floris-
sant. According to the theory outlined above the Mascall
beds of Oregon, which possess a varied flora, should be
either contemporaneous or (more probably) somewhat
earlier. Fortunately, fourteen species of mammals have
been obtained from the Mascall, and these place it rather
definitely in the Middle Miocene. Considering, therefore,
a probable moderate difference in time, combined with
noteworthy geographical and altitudinal differences, we
ought to find the Mascall flora similar to, but by no means
identical with, that of Florissant ; and this is exactly what
Thus of the 77 Mascall plants (nearly all trees) re-
ferred to definite genera, no less than 56 are congeneric
with those of Florissant. Of those not congeneric, five
are so dubious that they have not been specifically deter-
mined. The Mascall genera not yet found at Florissant
are the following:
1. Equisetum.— This has no significance, as it abounds
in Colorado to-day, and must have been present during
the Florissant period.
No. 517] MIOCENE TREES 35
2. Ginkgo.— Represented in the Mascall by a fragment
not specifically determined. This genus is not known
in the Rocky Mountains later than the Laramie and Liv-
ingston, on the border line between the Cretaceous and
Tertiary. As is well known, there is a single living
3. Thuites.—A fragment not specifically determined.
It is practically identical with T. elireuswardi Heer
(Miocene of Sachalin and Spitsbergen), but that plant
appears to be referable to the modern genus Chamrecy-
4. Glyptostrob'iis.—A genus still living in China. It
was supposed to occur at Florissant, but I believe the
material so referred all belongs to Sequoia. The Mascall
material is not above suspicion of also being Sequoia;
indeed Lesquereux so referred one of the specimens.
5. Taxodiwn. — The Mascall specimens are referred by
Knowlton to the widely distributed T. disticlmm mio-
cenum Heer, which should be called Tax odium disticlmm
dubium = Taxodinm dubium (Sternb.) Heer, originally
described from Bilin. This differs from Sequoia by the
deciduous leaves, which are not decurrent at the base as
in Glyptostrobus. The genus still lives in our southern
6. Artocarpiis.—'ReipTesented by very fragmentary
material, doubtfully referred to A. californica Kn.
7. Magnolia.— Major Bendire collected a plant which
Knowlton says "may well be" M. ingle fi-eldi Heer. It
has not been obtained by recent collectors. Magnolia
dayana Ckll. ined. (M. lanceolata Lx. 1878, not Link.
1831) is listed by Knowlton as from the Mascall, but in
his detailed account he says it is from Cherry Creek,
which should be Lower Eocene.
8. Lawns.— Florissant has a species of Persea ; Lauras
and Persea are allied, and not distinctly separated by
9. Platanus.—The Mascall specimens appear to belong
THE AMERICAN NATURALIST [Vol. XLIV
ffih t 3? '
^r^kmmmm ' A
Jkk jlffr \kSfc Mir
^L m^ pi ' jjr ^*
• v^ *d
Fig. 3. Sequoia hayileni (Lesquereux). Redwood.
to three species, but none are sufficiently well preserved
for positive specific identification.
10. Pnmus.— The two Mascall species described by
Knowlton are only doubtfully referred to this genus,
which is of course abundant in the modern flora.
11. Rulac— Generic reference rather uncertain; the
genus is scarcely separable from Acer, which occurs at
12. 2E sculus.— This well-known living genus is repre-
No. 517] MIOCENE TREES 37
sented in the Mascall by leaflets which closely resemble
an nnclescribed Florissant species which may be a Ber-
beris, but is certainly not an iE senilis.
13. (jren'ia. — The Mascall plant is referred by Knowl-
ton to U. crenata (linger) Heer, which occurs in Europe
at (Eningen. 4
Three other genera, Phragmites, Oyperacit.es and
Smilax, are non-arborescent, and have no particular sig-
Tims it would appear that in the Middle Miocene
period Ginkgo and Glyptostrobns— if we may accept the
determinations— had not yet retreated from the Amer-
ican continent, but survived at least in the northwest.
For the rest, the Mascall flora is no doubt a lowland one
as compared with that of Florissant, and this alone would
explain many of the differences ; thus, no one would ex-
pect to find Taxodinm growing around a mountain lake.
Dr. Knowlton has described (Monog. II. S. Geol. Sur-
vey, Vol. 32, part 2) an extensive flora from the Yellow-
stone, which he regards as Miocene. The fossil plants
of the Yellowstone National Park are divided by him into
three series: (1) Fort Union, which is Basal Eocene,
(2) Intermediate, said to be Miocene, and (3) Lamar
Flora, also Miocene. With the first we are not now con-
cerned, but the others must be compared with the flora
of Florissant. Considering the relative proximity of the
Yellowstone beds to those of Colorado, one would expect
to find much similarity and even identity in the plants ;
but this is not the case. The difference of locality, with
a moderate difference in time, might perhaps account for
the diversity of species; but the Yellowstone flora as a
whole does not impress one as being so modern as that
of the Mascall beds or Florissant, while there is a sig-
nificant identity of species with those of the Eocene.
I have extracted from Knowlton 7 s tables a list of all
the Yellowstone "Miocene" plants said to occur else-
where or in the Eocene, with the following result:
4 The African Grewia crenata Hoclist., 18(38 (not linger, 1850), takes tlie
name G. po-pulifolia Vahl, 1790.
THE AMERICAN NATURALIST [Vol. XLIV
Fig. 4. Rhus coriarioides Lesquereux. Sumach.
1. Common to Fort Union (Eocene), Intermediate
Sequoia langsdorfii (Brgt.). Said to go down to
the Laramie (Cretaceous).
Juglans rugosa Lx. Goes down to the Laramie.
Castanea pulchella Kn.
Ficus densifolia Kn.
Lmirus calif omica Lx. Also auriferous gravels
Lmirus grandis Lx. (not Wallich). Also aurif-
erous gravels of California.
Platanns guillelmcd Gopp. Perhaps also Laramie.
Aralia notata Lx. Also Denver beds.
* Elceodendron polymorphtim Ward.
2. Common to Fort Union and Intermediate.
Equisetum canalicidatum Kn. Perhaps also in the
No. 517] MIOCENE TREES 39
Magnolia (?) pollardi Kn.
* Ulmtis minima Ward?
Sapindus affinis Newby.
3. Common to Fort Union and Lamar.
Asplenium iddingsi Kn.
Lyg odium Jcaidfussi Heer„
Eq-uisetum decidmim Kn.
Juglans crescentia Kn.
Fiats asimincefolia Lx. Also auriferous gravels
Laurus prUnigenia linger?
Malapoenna lamarensis Kn.
Sapindus grcmdifoliohis "Ward.
Sapindus warclii Kn.
* Ilicoria antiqiia (Newt).).
*Ulmus pseudofidva Lx.?
Those marked with an asterisk occur in the Fort Union
only outside of the Yellowstone.
4. Common to the Intermediate and the Denver beds
Osmunda affinis Lx.
5. Common to the Lamar, Basal Eocene and Laramie.
Rhammis rectinervis Heer, Lx. Heer describes
this from Monod, in the Lower Miocene ; we may
venture to doubt the identity of the American
Thus we have twenty-six plants specifically identical
with those of the Basal Eocene. 5
6. Common to Lamar and "Green River" of Knowlton.
(See also under 7.)
Salix elongata 0. Web. Said to occur at Elko
Station, Nevada, but represented only by un-
characteristic fragments. The determination of
5 The Mascall is supposed to have five species common to the Fort Union;
but of these two are doubtful, two others are the conifers Sequoia Jangs-
clorfii and Tax odium, while the fifth is Sapindus outusifolius, to which a
single specimen from the Mascall "seems to belong." S. obtusifolius was
originally described from beds supposed to belong to the Washakie (Later
THE AMERICAN NATURALIST [Vol. XLIV
Fig. 5. Ulmus hilliw Lesquereux. Elm.
the Lamar plant is considered doubtful by
Fagus (Fagopsis) longifolia (Lx.). Elko Station,
Nevada; Florissant (very abundant) and
Eocene (?) of British Columbia. The British
Columbia locality is on the Similkameen River,
whence come various fossil insects. Dr. Daw-
son (quoted by Scudder) considered these de-
posits Miocene. The Yellowstone collection in-
cludes about forty specimens which Knowlton
No. 517] MIOCENE TREES 41
refers here, all from Fossil Forest Ridge. Thi
is, undoubtedly, a distinctively Miocene plant,
and must be accepted as pertinent evidence.
The determination must be presumed to be
correct, though it may be pointed out that
various other leaves have almost exactly
the same venation and appearance. This is
especially true of the species of Zelkova, to
which genus Engler (1894) actually referred
F. longifolia, though the discovery of the fruit
has since shown that it is not related thereto.
Vlmus plw'inervia, as figured by Heer from
Alaska, is also almost exactly like F. longifolia;
it is considered doubtfully Eocene, but Knowl-
ton has recognized it in the Mascall (Miocene).
From the shape of the base, and other features,
it seems to me certain that the Alaskan plant is
not the original U. plurincrvia, of which linger
gives four figures in the Chloris Protogsea. The
latter is decidedly more elm-like in appearance.
Con/his macquarrii (Forbes) Heer. This plant,
as recognized in America, is a Fort Union and
possibly Laramie species ; recorded also from
the Eocene (?) of Alaska.
Diospyros hracliysepala A. Br. As recognized in
this country, this is a Laramie and Fort Union
species; the record from Florissant I believe to
None of the above belong to the genuine Green River
series ; three are quite without significance as indicating
Miocene affinities, but the Fag us stands out as a solitary
7. Common to the Lamar and the Auriferous gravels
of California. (See also under 1 and 3.)
Juglans leonis Ckll. Two specimens in the Lamar.
Popuhis balsamoides Gopp. Also Miocene (?) of
Alaska. Known in the Yellowstone only from
a fragment, which certainly can not be positively
determined as balsamoides: in fact, it shows
THE AMERICAN NATURALIST [Vol. XLIV
Fig. 6. Myrica drymeja (Lesquereux).
some differences, at least as compared with the
original European balsamoides, which ought to
Salix varians Gopp. Eocene (?) of Alaska. The
Lamar plant is a fragment, and according to the
figure, the margin is quite unlike that of the
Salix angusta A. B. Said to occur also in. the
Basal Eocene and true Green River. The
Lamar material consists of doubtful fragments.
Quercus furcinervis americana Kn.
Ficus shastensis Lx. ?
Ficus sordida Lx. A mere fragment from the
Ficus asimincefolia Lx. Very indifferent material
from the Lamar. Also Fort Union.
Magnolia calif ornica Lx.? The Lamar plant is
represented by a single specimen, "so much
No. 517] MIOCENE TBEES 43
broken that its positive identification is not pos-
Per sea pseudocarolinensis Lx. The Lamar speci-
men figured, "the best one found," consists of
the upper half of a leaf ; what there is of it ap-
pears to agree with the Californian species, al-
though it has more lateral viens.
Rhus mixta Lx.?
Aralia ivhitneyi Lx. Also in the Intermediate.
None of the Yellowstone specimens are perfect,
but they appear to belong to this handsome
Thus the species common to the Lamar and Auriferous
gravels, but not known from Basal Eocene, are few, and
in several cases of doubtful identity. As the reference
of the Lamar to the Miocene rests wholly on the resem-
blance of the flora to that of the Auriferous gravels, with
the exception of the indication afforded by Fagus longi-
folia, it must be considered at least somewhat dubious.
It is also to be remarked that eleven species of plants are
supposed to be common to the Yellowstone Fort Union
and the Auriferous gravels, although two of these, at
least, are doubtfully from the gravels, while in four or
five cases the Yellowstone material is fragmentary or
It is one thing, however, to recognize distinct elements
in common between the Auriferous gravels and the
Lamar, and another to prove the latter Miocene thereby.
The former may be conceded, the latter I think not.
Lesquereux enumerates thirteen species from the Au-
riferous gravels which are almost identical with living
species ; he also cites seventeen which are evidently, but
not very closely, related to living ones. Of the thirteen,
four are enumerated from the -Lamar; of the seventeen,
not one. Of the four common to the Lamar, three are
dubious, and only Juglans leonis (a species represented
to-day by the Asiatic J. regia) appears to be of satis-
THE AMERICAN NATURALIST [Vol. XLIV
Fig. 7. Populus crassa (Lesquereux). Cottonwood;
probably fruit of P. lesqucrcuxi.
Fig. 8. Populus lesquereuxi Ckll. Cottonwood.
Four species of the Auriferous gravels are said by
Lesquereux to be identical with Miocene plants, but are
all unsatisfactory, as follows: (1) Fag us antipofii; per-
haps goes to the Laramie, and the Californian specimen
was only half a leaf. (2) Populus zaddachi; supposed
to go down to the Basal Eocene. (3) Ficus tilicefolia;"
Fig. 0. Salix ramaleyi Ckll. Willow.
c Ficus tilicefolia (A. Br.) Heer, 1856, has priority over F. tilicefolia
Baker, Jn. Linn. Soc. 21: 443 (1885), from Madagascar. The latter may
become Ficus oakeriana n. n.
No. 517] MIOCENE TREES 45
said to go down to the Laramie. (4) Aralia zaddachi;
of uncertain determination, one of the specimens was
Platanus dissecta. None of these is found in the Lamar,
hut F.antipofii is in the Yellowstone Fort Union.
Bight other species from the Auriferous gravels are
stated to he allied to Miocene species, five of these being
also related to living plants. One of the five, Juglans
oregoniana, has since proA T ed to he from the Mascall, and
not to occur in the Auriferous gravels. The other three
are as follows :
Fic-us sordida Lx. Allied to, or perhaps identical
with, F. grmnlandica of Greenland. A frag-
ment referred to this has been found in the
Ficus menscc n. n. (F. micropliylla Lx., 1878, not
Salzm., Mart. Fl. Braz. 4: 93). Allied to F.
planicostata '—but this is a species of the Basal
Eocene and Laramie.
Aralia wliitneg-i Lx., said to be allied to an Evans-
ton species, which would be Eocene.
It is thus apparent that the Auriferous gravels flora
has no decisive Miocene affinities, but is composed of two
sets of plants, one related to living forms, the other to
those of the Eocene. It is known to be a mixed lot, and
when I recently suggested to Dr. J. C. Merriam, of the
"University of California, that it might perhaps be partly
Pliocene and partly Eocene, he replied that this might
indeed be the case.
It is further to be remarked that Knowlton formerly
regarded the Mascall flora as having affinity with that of
the Auriferous gravels; but he subsequently discovered
that certain of the species he had most relied on were
really confined to the Mascall, and did not occur in the
gravels at all. "This correlation therefore fails," he
states, and the absence of relationship stands as an argu-
ment against the Miocene age of the gravels.
The conclusion seems to be legitimate that the Yellow-
stone Intermediate and Lamar florae are Upper Eocene,
or at least older than Miocene. Were they really Mio-
THE AMERICAN NATURALIST [Vol. XLIV
Fig. 10. Ptelea modcsta (Lesquereux). Fig. 11. Melia expulsa Ckll.
cene, with so much resemblance to even the Basal Eocene,
the Florissant flora, to get as far on the other side as its
lack of affinity would suggest, would have to be projected
somewhere into the future! If this opinion is in any
degree correct, Florissant remains as the only Rocky
Mountain locality for Miocene plants, so far as known.
The accompanying figures, all taken from specimens
obtained at Florissant by the University of Colorado ex-
peditions, will give a good idea of the material from that
locality. Nowhere else in America are Tertiary plants
so well preserved. As compared with the Eocene flora,
and especially the Basal Eocene, the Florissant trees
are more diverse in type, with usually smaller leaves,
which are often compound. Excessively moist condi-
tions are not indicated, though there was evidently much
more moisture than at the present day. Some of the
plants are even somewhat xerophytic, indicating that the
higher slopes may have been relatively dry. Osborn
remarks on the evidence of increasing summer droughts
No. 517] MIOCENE TREES 47
in the Middle Miocene. So far as the mammals are con-
cerned, this is chiefly indicated by the plains fauna. Ow-
ing to the generally higher temperature, the air was
probably moister than at present, but the moisture may
have carried farther, to be precipitated on the mountains.
Thus the conditions on the plains and towards the sea
may have resembled those of Southern and Lower Cali-
fornia to-day, with a comparatively damp atmosphere but
little or no preciptation during a considerable part of
the year. The desert fauna and flora of the southwest
is a highly specialized one, which has certainly not come
into existence since the Miocene, at least as regards its
fundamental types; so it becomes necessary to postulate
a desert region during Miocene times, and no doubt much
earlier. Whether we shall ever know much about the
Tertiary deserts from fossil remains is perhaps question-
able, though we certainly have evidence of a semi-desert
fauna, as is illustrated by the large tortoises of the Upper
Miocene. The Florissant beds afford us a wonderful
insight into the mountain life of the Miocene, and must
have a continually increasing significance in relation to
the evolution of the fauna and flora of this continent.
Most unfortunately, they have as yet yielded no recogniz-
able mammalian remains, but I am convinced that these
will eventually be found. The beds are far from being
exhausted, and comparatively little digging has been
done at the place where fragments of a mammal were
obtained— a locality which I shall be glad to describe in
detail to any one who cares to go and try his luck. In
the meanwhile, large collections both of plants and of in-
sects, already obtained, remain to be investigated and re-
ported upon, but for various reasons the work proceeds